Many devices of this type are already known from the prior art.
However, the present invention provides a structure which is simple to implement and which allows in particular, according to one preferred embodiment, provision of up to four different axial positions of the stem with only two movable contact elements necessary to distinguish between these different positions.
U.S. Pat. No. 6,203,190, issued 20th Mar. 2001 in the name of Timex, describes an electronic stem having four different axial positions. To this end it is provided that the stem comprises an annular groove, in which is fitted a tongue integral with a contact collar mounted, near to the stem, rotatably about an axis orthogonal to the axis of the stem. When the stem is displaced into its different axis positions, the groove entrains the tongue, whose displacement causes the contact collar to rotate. Moreover the collar carries a second tongue, whose free end is located opposite a plurality of electric contact pads which are formed at the end of electrically conductive tracks. When the contact collar turns in response to axis displacement of the stem, the second tongue moves from one contact pad to the other, the second tongue being so shaped that its free end is disposed in contact with the contact pads.
The structure of the control device shown in this patent is however complex to realise, in particular because of the number of different elements which are needed for its operation and because the relative positioning of some of these elements needs to be precise. Furthermore, this structure has a significant size and requires implementation of an electric contact track-pad assembly for each axial position of the stem. Moreover the device described can exhibit problems of wear related to poor ageing with time because of its mode of operation. Thus, a plurality of constituent elements of this device are arranged to slide while rubbing on one another—the contact collar on its support and the free end of the second tongue on the contact pads—which gives rise to significant wear in the course of operation. Furthermore the rubbing can release small particles of matter which are prone to interfere with the operation of the device in the long term.